1 files changed, 23 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 7caed0006ee7..6e2acfd687a1 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -1028,6 +1028,12 @@ static uint16_t vlv_compute_wm_level(const struct intel_crtc_state *crtc_state,
         return min_t(int, wm, USHRT_MAX);
 }
 
+static bool vlv_need_sprite0_fifo_workaround(unsigned int active_planes)
+{
+        return (active_planes & (BIT(PLANE_SPRITE0) |
+                                 BIT(PLANE_SPRITE1))) == BIT(PLANE_SPRITE1);
+}
+
 static int vlv_compute_fifo(struct intel_crtc_state *crtc_state)
 {
         struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
@@ -1038,12 +1044,25 @@ static int vlv_compute_fifo(struct intel_crtc_state *crtc_state)
         int num_active_planes = hweight32(active_planes);
         const int fifo_size = 511;
         int fifo_extra, fifo_left = fifo_size;
+        int sprite0_fifo_extra = 0;
         unsigned int total_rate;
         enum plane_id plane_id;
 
+        /*
+         * When enabling sprite0 after sprite1 has already been enabled
+         * we tend to get an underrun unless sprite0 already has some
+         * FIFO space allcoated. Hence we always allocate at least one
+         * cacheline for sprite0 whenever sprite1 is enabled.
+         *
+         * All other plane enable sequences appear immune to this problem.
+         */
+        if (vlv_need_sprite0_fifo_workaround(active_planes))
+                sprite0_fifo_extra = 1;
+
         total_rate = raw->plane[PLANE_PRIMARY] +
                 raw->plane[PLANE_SPRITE0] +
-                raw->plane[PLANE_SPRITE1];
+                raw->plane[PLANE_SPRITE1] +
+                sprite0_fifo_extra;
 
         if (total_rate > fifo_size)
                 return -EINVAL;
@@ -1064,6 +1083,9 @@ static int vlv_compute_fifo(struct intel_crtc_state *crtc_state)
                 fifo_left -= fifo_state->plane[plane_id];
         }
 
+        fifo_state->plane[PLANE_SPRITE0] += sprite0_fifo_extra;
+        fifo_left -= sprite0_fifo_extra;
+
         fifo_state->plane[PLANE_CURSOR] = 63;
 
         fifo_extra = DIV_ROUND_UP(fifo_left, num_active_planes ?: 1);